Process for producing acetoxy-bearing siloxanes

ABSTRACT

Described is a process for producing trifluoromethanesulfonic acid-acidified, end-equilibrated, acetoxy-bearing siloxanes which comprises reacting cyclic siloxanes, in particular comprising D 4  and/or D 5 , and/or cyclic branched siloxanes of the D/T type with acetic anhydride using trifluoromethanesulfonic acid as catalyst and with addition of acetic acid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 119 patent application which claimsthe benefit of European Application No. 18189073.2 filed Aug. 15, 2018,which is incorporated herein by reference in its entirety.

FIELD

The present invention relates to a process for producingtrifluoromethanesulfonic acid-acidified, end-equilibrated,acetoxy-bearing siloxanes.

BACKGROUND

As reactive starting materials for producing SiOC-based siliconederivatives, in particular SiOC-based polyether siloxanes,acetoxy-bearing siloxanes having linear or branched structure type areimportant compound classes.

The as yet unpublished European patent applications having theapplication numbers EP18172882.5, EP18172876.7, EP17195510.7 andEP17204277.2 are concerned with the production of SiOC-bonded polyethersiloxanes, wherein trifluoromethanesulfonic acid-acidified, equilibratedacetoxysiloxanes having linear or branched structure type are used asreactive intermediates.

On closer investigation of the modes of production recited in thesedocuments for producing the acetoxysiloxanes used therein the inventorshave found that immediately after their production thetrifluoromethanesulfonic acid-acidified acetoxysiloxanes still compriserelatively large proportions of siloxane cycles (see to this endexamples 3 and 6 of the present invention) which, however, upon storageof the siloxanes at 23° C. over the course of about 2 to 3 weeks becomeincorporated in the respective siloxane matrix in such a way that thecontent of remaining siloxane cycles (D₄+D₅+D₆) corresponds to the endequilibrium established at this temperature and a pressure of 1013.25hPa.

The trifluoromethanesulfonic acid-acidified, equilibratedacetoxysiloxanes resulting therefrom thus meet all quality demands thatmay be placed on these reactive intermediates. However, it remainsdesirable to achieve improved kinetics of equilibration to allowimmediate further processing of the intermediates.

SUMMARY

Against this background the present invention has for its object toprovide a process for producing end-equilibrated acetoxy-bearingsiloxanes which advantageously accelerates the kinetics of equilibrationsuch that reactive siloxanes capable of immediate further processing arealready isolated at the end of the production process.

DETAILED DESCRIPTION

It has now been found in the context of the present invention that,surprisingly, end-equilibrated acetoxysiloxanes of both linear andbranched structure type are obtainable when the reactions described inthe as yet unpublished European patent applications having theapplication numbers EP18172882.5, EP18172876.7, EP17195510.7 andEP17204277.2 are implemented with addition of acetic acid.

The present invention provides a process for producingtrifluoromethanesulfonic acid-acidified, end-equilibrated,acetoxy-bearing siloxanes which comprises reacting cyclic siloxanes, inparticular comprising D₄ and/or D₅, and/or mixtures of cyclic branchedsiloxanes of the D/T type with acetic anhydride usingtrifluoromethanesulfonic acid as catalyst and with addition of aceticacid.

In terms of the usability of DT cycles the inventors have found that notonly mixtures of cyclic branched siloxanes of the D/T type which consistexclusively of siloxanes comprising D and T units and whose ²⁹Si NMRspectroscopy-determinable cumulative proportion of D and T unitscomprising Si-alkoxy and/or SiOH groups present in the siloxane matrixis less than 2 mole percent, preferably less than 1 mole percent, andwhich advantageously further contain at least 5% by weight of siloxanecycles, such as preferably octamethylcyclotetrasiloxane (D₄),decamethylcyclopentasiloxane (D₅) and/or mixtures thereof, but alsomixtures of cyclic branched siloxanes comprising exclusively D and Tunits whose ²⁹Si NMR spectroscopy-determinable cumulative proportion ofD and T units comprising Si-alkoxy and/or SiOH groups present in thesiloxane matrix is greater than 2 and less than 10 mole percent areparticularly suitable for use according to the invention.

The cyclic branched siloxanes of the D/T type usable according to theinvention are not only described by way of example in the experimentalpart but also described in detail in the European patent applicationEP3321304A1 and in the as yet unpublished patent application EP17169876.4. Both documents are accordingly incorporated in theirentirety into the disclosure content of this invention.

Suitable for obtaining the mixtures of cyclic branched siloxanescomprising exclusively D and T units whose ²⁹Si NMRspectroscopy-determinable cumulative proportion of D and T unitscomprising Si-alkoxy and/or SiOH groups present in the siloxane matrixis greater than 2 and less than 10 mole percent is a process comprisingthe steps of

-   -   (a) an acid-catalysed equilibration of trialkoxysilanes with        siloxane cycles and/or α,ω□□-dihydroxypolydimethylsiloxane in        the presence of at least one acidic catalyst and then    -   (b) a hydrolysis and condensation reaction initiated by addition        of water, and addition of a silicon-containing solvent, followed        by    -   (c) a distillative removal of the alcohol released, of water        present in the system and of silicon-containing solvent, and a        neutralization or removal of the acidic catalyst and optionally        removal of salts that have possibly formed,    -   wherein the silicon-containing solvent preferably comprises the        isomeric siloxane cycles octamethylcyclotetrasiloxane (D₄),        decamethylcyclotetrasiloxane (D₅) and/or mixtures thereof and        mass ratios of silicon-containing solvent to the siloxane        comprising D and T units of 1:1 to 5:1 are advantageously        employed        as described in the as yet unpublished patent application EP        17169876.4.

Shown hereinbelow by way of example for the sake of enablement is theproduction of these abovementioned mixtures of cyclic branched siloxanescomprising exclusively D and T units: In a 500 ml four-neckedround-bottomed flask with a KPG stirrer and fitted with a reflux cooler,52.2 g (0.293 mol) of methyltriethoxysilane are heated to 60° C.together with 130.3 g (0.351 mol) of decamethylcyclopentasiloxane whilestirring, 0.400 g of trifluoromethanesulfonic acid is added and themixture is equilibrated for 4 hours. Then 15.8 g of water and 4.0 g ofethanol are added and the mixture is heated to reflux temperature (about80° C.) for a further 4 hours. 10.6 g of water and 200 ml ofdecamethylcyclopentasiloxane (D5) are added and the reflux cooler isexchanged for a distillation bridge, and the constituents that arevolatile up to 90° C. are distilled off within the next hour. Thereaction mixture is left at 90° C. for a further 2 hours, then allowedto cool down to 50° C., and 5 ml of a 25% aqueous ammonia solution areadded and the mixture is stirred for a further hour to complete theneutralization. At 100° C. and with an auxiliary vacuum of <1 mbarapplied, water and the decamethylcyclopentasiloxane (D₅) used as solventare distilled off. After cooling the distillation bottoms, with the aidof a pleated filter, the precipitated ammonium triflate is removed. Thefiltrate is a colorless mobile liquid, whose ²⁹Si NMR spectrum shows aD/T ratio of 6.1:1 (target 6.0:1). Based on the sum of the Si unitsdetected by spectroscopy, the D and T units bearing Si-alkoxy and SiOHgroups respectively have a proportion of 4.1 mole percent.

Suitable for obtaining the mixtures of cyclic branched siloxanes of theD/T type which consist exclusively of siloxanes comprising D and T unitsand whose ²⁹Si NMR spectroscopy-determinable cumulative proportion of Dand T units comprising Si-alkoxy and/or SiOH groups present in thesiloxane matrix is ≤2 mole percent, preferably less than 1 mole percent,and which advantageously further contain at least 5% by weight ofsiloxane cycles, such as preferably octamethylcyclotetrasiloxane (D₄),decamethylcyclopentasiloxane (D₅) and/or mixtures thereof, is a processin which a trialkoxysilane is reacted in a solvent with siloxane cyclesand/or α,ω-dihydroxypolydimethylsiloxane with addition of water and inthe presence of at least one acidic catalyst as described in Europeanpatent application EP3321304A1. Example 1 of the present invention showsby way of example the production of corresponding mixtures of cyclicbranched siloxanes of the D/T type.

A preferred embodiment of the invention comprises adding acetic acid inamounts of 0.4 to 3.5 percent by weight, by preference 0.5 to 3 percentby weight, preferably 0.8 to 1.8 percent by weight, particularlypreferably in amounts of 1.0 to 1.5 percent by weight, based on thereaction matrix consisting of acetic anhydride and cyclic siloxanescomprising D₄ and/or D₅ or consisting of acetic anhydride and mixturesof cyclic branched siloxanes of the D/T type or consisting of cyclicsiloxanes comprising D₄ and/or D₅ and mixtures of cyclic branchedsiloxanes of the D/T type.

In a preferred embodiment of the invention the catalysttrifluoromethanesulfonic acid is employed in amounts of 0.1 to 1.0percent by mass, preferably 0.1 to 0.3 percent by mass, based on thereaction matrix consisting of acetic anhydride and cyclic siloxanes, inparticular comprising D₄ and/or D₅, and/or cyclic branched siloxanes ofthe D/T type.

The term “end-equilibrated” is to be understood as meaning that theequilibrium established at a temperature of 23° C. and a pressure of1013.25 hPa has been reached. Employable as an indicator for reachingthe equilibrium is the total cycles content determined by gaschromatography and defined as the sum of the D₄-, D₅-, D₆-contents basedon the siloxane matrix and ascertained after derivatization of theα,ω-diacetoxypolydimethylsiloxanes to the correspondingα,ω-diisopropoxypolydimethylsiloxanes or after derivatization of thebranched acetoxysiloxanes to the corresponding branchedisopropoxysiloxanes. The inventive use of acetic acid here makes itpossible to readily undershoot otherwise customary equilibriumproportions of about 13 percent by weight of total cycles content forthe linear α,ω-diacetoxypolydimethylsiloxanes and of about 8 percent byweight of total cycles content for the branched acetoxysiloxanes. It istherefore in accordance with a preferred embodiment when equilibriumproportions of the total cycles content of less than 13, preferably lessthan 12, percent by weight for the linearα,ω-diacetoxypolydimethylsiloxanes and equilibrium proportions of thetotal cycles content of less than 8, preferably less than 7, percent byweight for the branched acetoxysiloxanes are undershot. Thederivatization to afford the α,ω-diisopropoxypolydimethylsiloxanes or toafford the branched isopropoxysiloxanes is intentionally chosen in orderto prevent a thermally induced retrocleavage reaction of theα,ω-diacetoxypolydimethylsiloxanes or of the branched acetoxysiloxaneswhich may take place under the conditions of analysis by gaschromatography (regarding the retrocleavage reaction see inter alia J.Pola et al., Collect. Czech. Chem. Commun. 1974, 39(5), 1169-1176 andalso W. Simmler, Houben-Weyl, Methods of Organic Chemistry, Vol. VI/2,4th Edition, 0-Metal Derivates of Organic Hydroxy Compounds p. 162 ff)).

In a preferred embodiment the reaction is carried out in a temperaturerange of 140° C. to 160° C. and over a duration of 4 to 8 hours.

The present invention further relates to trifluoromethanesulfonicacid-acidified, end-equilibrated linear α,ω-acetoxy-bearing siloxaneshaving total cycles contents defined as the sum of the content fractionsof the cyclic siloxanes comprising D₄, D₅ and D₆ based on the siloxanematrix and determined by gas chromatography after their derivatizationto afford the corresponding linear α,ω-isopropoxysiloxanes of less than13, preferably less than 12, percent by weight, preferably produced by aprocess according to the invention as described above.

The present invention further relates to trifluoromethanesulfonicacid-acidified, end-equilibrated branched acetoxy-bearing siloxaneshaving total cycles contents defined as the sum of the content fractionsof the cyclic siloxanes comprising D₄, D₅ and D₆ based on the siloxanematrix and determined by gas chromatography after their derivatizationto afford the corresponding branched isopropoxysiloxanes of less than 8,preferably less than 7, percent by weight, preferably produced by aprocess according to the invention as described above.

The present invention further relates to the use of the end-equilibratedtrifluoromethanesulfonic acid-acidified acetoxy-bearing siloxanes asdescribed above as starting materials for the production of SiOC-bondedpolyether siloxanes for use thereof in PU foam stabilizers, indefoamers, in demulsifiers, in emulsifiers and in paint and flow controladditives.

EXAMPLES

The examples which follow are provided merely to elucidate thisinvention to those skilled in the art and do not constitute anylimitation of the claimed subject matter whatsoever. The determinationof water contents is in principle performed by the Karl Fischer methodbased on DIN 51777, DGF E-III 10 and DGF C-III 13a. ²⁹Si-NMRspectroscopy was used for reaction monitoring in all examples.

In the context of the present invention the ²⁹Si NMR samples areanalysed at a measurement frequency of 79.49 MHz in a Bruker Avance IIIspectrometer equipped with a 287430 sample head with gap width of 10 mm,dissolved at 22° C. in CDCl₃ and against a tetramethylsilane (TMS)external standard [δ(²⁹Si)=0.0 ppm].

GPCs (gel permeation chromatography) are recorded using THF as themobile phase on an SDV 1000/10000A column combination having a length of65 cm, ID 0.80, at a temperature of 30° C. using a SECcurity² GPC System1260 (PSS Polymer Standards Service GmbH).

The gas chromatograms are recorded on an Agilent Technologies GC 7890BGC instrument fitted with an HP-1 column having dimensions of 30 m×0.32mm ID×0.25 μm dF (Agilent Technologies No. 19091Z-413E) using hydrogenas a carrier gas and employing the following parameters:

Detector: FID; 310° C.

Injector: Split; 290° C.

Mode: constant flow, 2 ml/min

Temperature programme: 60° C. at 8° C./min-150° C. at 40° C./min-300° C.10 min.

Employed as an indicator for reaching the equilibrium is the totalcycles content determined by gas chromatography and defined as the sumof the D₄-, D₅-, D₆-contents based on the siloxane matrix andascertained after derivatization of theα,ω-diacetoxypolydimethylsiloxanes to the correspondingα,ω-diisopropoxypolydimethylsiloxanes. The derivatization to afford theα,ω-diisopropoxypolydimethylsiloxanes is intentionally chosen in orderto prevent a thermally induced retrocleavage reaction of theα,ω-diacetoxypolydimethylsiloxanes which may take place under theconditions of analysis by gas chromatography (regarding theretrocleavage reaction see inter alia J. Pola et al., Collect. Czech.Chem. Commun. 1974, 39(5), 1169-1176 and also W. Simmler, Houben-Weyl,Methods of Organic Chemistry, Vol. VI/2, 4th Edition, 0-Metal Derivatesof Organic Hydroxy Compounds p. 162 ff)).

Example 1

Production of a Cyclic Branched Siloxane Having a Target D/T Ratio of6:1

In a 101 four-necked round-bottomed flask with a KPG stirrer and fittedwith a reflux cooler 783 g (4.39 mol) of methyltriethoxysilane togetherwith 978.7 g (2.64 mol) of decamethylcyclopentasiloxane are heated to60° C. with stirring, admixed with 2.98 g of trifluoromethanesulfonicacid and the mixture is equilibrated for 4 hours. 237 g of water and59.3 g of ethanol are then added and the batch is heated to refluxtemperature for a further 2 hours. 159.0 g of water and 978.8 g (2.64mol) of decamethylcyclopentasiloxane (D₅) are added and the refluxcooler is exchanged for a distillation bridge and the constituents thatare volatile up to 90° C. are distilled off over the next hour. 3000 mlof toluene are then added to the reaction batch and the water stillpresent in the system is removed by distillation up to a bottomstemperature of 100° C. at the water separator. The reaction mixture isallowed to cool to about 60° C., the acid is neutralized by addition of60.0 g of solid sodium hydrogencarbonate, and the mixture is thenstirred for a further 30 minutes to achieve complete neutralization.After cooling to 25° C. the salts are removed with the aid of a pleatedfilter.

At 70° C. and with an auxiliary vacuum of <1 mbar applied, the tolueneused as solvent is distilled off. The distillation bottoms are acolorless mobile liquid, whose ²⁹Si NMR spectrum shows a D/T ratio of6.2:1 (target 6.0:1). Based on the sum of the Si units detected byspectroscopy, the D and T units bearing Si-alkoxy and SiOH groupsrespectively, have a proportion of 0.52 mole percent. The gaschromatography analysis of the liquid also shows a proportion of about15 percent by weight of simple siloxane cycles in the form of D₄, D₅ andD₆. The GPC has a broad molar mass distribution, characterized by Mw=55258 g/mol; Mn: 1693 g/mol and Mw/Mn=32.63.

Example 2 (Inventive)

Production of an Acetoxy-Terminated, Branched Siloxane with 1.5% AceticAcid Addition

In a 1000 ml four-necked flask with a KPG stirrer, internal thermometerand fitted with a reflux cooler 49.9 g (0.489 mol) of acetic anhydridetogether with 268.1 g of the DT cycles produced in example 1 (D/T ratioaccording to ²⁹Si-NMR spectrum=6.18:1, M=525.42 g/mol and a proportionof SiOH/SiOEt moieties of 0.52 mol %) and 188.5 g ofdecamethylcyclopentasiloxane (D₅) are initially charged with stirringand admixed with 1.03 g (0.56 ml) of trifluoromethanesulfonic acid (0.2%by mass based on the total batch) and 7.6 g of acetic acid (1.5% basedon the mass of the reactants) and swiftly heated to 150° C. Theinitially slightly cloudy reaction mixture is held at this temperaturefor 6 hours with continued stirring.

After cooling of the batch a colorless clear mobile liquid whose²⁹Si-NMR spectrum demonstrates the presence of Si-acetoxy groups in ayield of about 88.2% based on the employed acetic anhydride and thecomplete disappearance of spectroscopically detectable proportions ofSi-alkoxy and SiOH groups is isolated.

Conversion of the Branched Acetoxysiloxane into the CorrespondingBranched Isopropoxysiloxane for Analytical Characterization

Immediately after the synthesis in a 250 ml four-necked round-bottomedflask fitted with a KPG stirrer, internal thermometer and a refluxcooler 100.0 g of this trifluoromethanesulfonic acid-acidified,equilibrated branched □acetoxysiloxane are mixed together with 23.2 g ofa molecular sieve-dried isopropanol by stirring at 22° C. Gaseousammonia (NH₃) is then introduced to the reaction mixture until alkalinereaction (moist universal indicator paper) and the mixture is thenstirred at this temperature for a further 45 minutes. The precipitatedsalts are separated using a pleated filter.

A colorless, clear liquid is isolated, whose accompanying ²⁹Si-NMRspectrum demonstrates the quantitative conversion of the branchedacetoxysiloxane into a branched □isopropoxysiloxane.

An aliquot of this branched □isopropoxysiloxane is withdrawn andanalysed by gas chromatography. The gas chromatogram shows the followingcontents (reported in percent by mass):

Total Isopropanol D₄ D₅ D₆ (D₄-D₆) content 2.3% 1.4% 0.4% 4.1% 7.1%

Taking account of the isopropanol excess the contents of siloxane cycles(D₄, D₅ and D₆) are calculated solely based on the siloxane proportion.

Example 3 (Noninventive) Production of an Acetoxy-Terminated BranchedSiloxane

In a 1000 ml four-necked flask with a KPG stirrer, internal thermometerand fitted with a reflux cooler 49.9 g (0.489 mol) of acetic anhydridetogether with 268.1 g of the DT cycles produced in example 1 (D/T ratioaccording to ²⁹Si-NMR spectrum=6.18:1, M=525.42 g/mol and a proportionof SiOH/SiOEt moieties of 0.52 mol %) and 188.5 g ofdecamethylcyclopentasiloxane (D₅) are initially charged with stirringand admixed with 1.03 g (0.56 ml) of trifluoromethanesulfonic acid (0.2mass % based on the total batch) and rapidly heated to 150° C. Theinitially slightly cloudy reaction mixture is held at this temperaturefor 6 hours with continued stirring.

After cooling of the batch a colorless clear mobile liquid whose²⁹Si-NMR spectrum demonstrates the presence of Si-acetoxy groups in ayield of about 92.3% based on the employed acetic anhydride and thecomplete disappearance of spectroscopically detectable proportions ofSi-alkoxy and SiOH groups is isolated.

Conversion of the Branched Acetoxysiloxane into the CorrespondingBranched Isopropoxysiloxane for Analytical Characterization

Immediately after the synthesis in a 250 ml four-necked round-bottomedflask fitted with a KPG stirrer, internal thermometer and a refluxcooler 100.0 g of this trifluoromethanesulfonic acid-acidified,equilibrated branched acetoxysiloxane are mixed together with 23.2 g ofa molecular sieve-dried isopropanol by stirring at 22° C. Gaseousammonia (NH₃) is then introduced to the reaction mixture until alkalinereaction (moist universal indicator paper) and the mixture is thenstirred at this temperature for a further 45 minutes. The precipitatedsalts are separated using a pleated filter.

A colorless, clear liquid is isolated, whose accompanying ²⁹Si-NMRspectrum demonstrates the quantitative conversion of the branchedacetoxysiloxane into a branched □isopropoxysiloxane.

An aliquot of this branched □isopropoxysiloxane is withdrawn andanalysed by gas chromatography. The gas chromatogram shows the followingcontents (reported in percent by mass):

Total Isopropanol D₄ D₅ D₆ (D₄-D₆) content 2.03% 21.85% 0.83% 24.71%11.7%

Taking account of the isopropanol excess the contents of siloxane cycles(D₄, D₅ and D₆) are calculated solely based on the siloxane proportion.

Example 4 (Inventive)

Production of an Acetoxy-Terminated, Linear Polydimethylsiloxane with1.5% Acetic Acid Addition

In a 1000 ml four-necked flask fitted with a KPG stirrer, internalthermometer and a reflux cooler 77.3 g (0.757 mol) of acetic anhydridetogether with 732.8 g (1.98 mol) of decamethylcyclopentasiloxane (D₅)and 12.2 g of acetic acid (1.5% by weight based on the total mass of thereactants) are initially charged with stirring and admixed with 1.62 g(0.88 ml) of trifluoromethanesulfonic acid (0.2 percent by mass based onthe total batch) and swiftly heated to 150° C. The initially slightlycloudy reaction mixture is held at this temperature for 6 hours withcontinued stirring.

After cooling of the batch a colorless, clear, mobile liquid isisolated, whose ²⁹Si-NMR spectrum demonstrates the presence ofSi-acetoxy groups in a yield of about 93% based on employed aceticanhydride corresponding to an α,ω-diacetoxypolydimethylsiloxane havingan average total chain length of about 14.

Conversion of the α,ω-Diacetoxypolydimethylsiloxane into theCorresponding α,ω-Diisopropoxypolydimethylsiloxane for AnalyticalCharacterization

Immediately after the synthesis in a 250 ml four-necked round-bottomedflask fitted with a KPG stirrer, internal thermometer and a refluxcooler 50.0 g of this trifluoromethanesulfonic acid-acidified,equilibrated α,ω-diacetoxypolydimethylsiloxane are mixed together with11.3 g of a molecular sieve-dried isopropanol by stirring at 22° C.Gaseous ammonia (NH₃) is then introduced to the reaction mixture untilalkaline reaction (moist universal indicator paper) and the mixture isthen stirred at this temperature for a further 45 minutes. Theprecipitated salts are separated using a pleated filter.

A colorless, clear liquid is isolated, whose accompanying ²⁹Si-NMRspectrum demonstrates the quantitative conversion of theα,ω-diacetoxypolydimethylsiloxane into anα,ω-diisopropoxypolydimethylsiloxane.

An aliquot of this α,ω-diisopropoxypolydimethylsiloxane is withdrawn andanalysed by gas chromatography. The gas chromatogram shows the followingcontents (reported in percent by mass):

Total Isopropanol D₄ D₅ D₆ (D₄-D₆) content 4.94% 4.04% 1.07% 10.06%11.00%

Taking account of the isopropanol excess the contents of siloxane cycles(D₄, D₅ and D₆) are calculated solely based on the siloxane proportion.

Example 5 (Inventive)

Production of an Acetoxy-Terminated, Linear Polydimethylsiloxane with3.0% Acetic Acid Addition

In a 1000 ml four-necked flask fitted with a KPG stirrer, internalthermometer and a reflux cooler 77.3 g (0.757 mol) of acetic anhydridetogether with 732.8 g (1.98 mol) of decamethylcyclopentasiloxane (D₅)and 24.3 g of acetic acid (3.0% by weight based on the total mass of thereactants) are initially charged with stirring and admixed with 1.62 g(0.88 ml) of trifluoromethanesulfonic acid (0.2 percent by mass based onthe total batch) and swiftly heated to 150° C. The initially slightlycloudy reaction mixture is held at this temperature for 4 hours withcontinued stirring.

After cooling of the batch a colorless, clear, mobile liquid isisolated, whose ²⁹Si-NMR spectrum demonstrates the presence ofSi-acetoxy groups in a yield of about 93% based on employed aceticanhydride corresponding to an α,ω-diacetoxypolydimethylsiloxane havingan average total chain length of about 14.

Conversion of the α,ω-Diacetoxypolydimethylsiloxane into theCorresponding α,ω-Diisopropoxypolydimethylsiloxane for AnalyticalCharacterization

Immediately after the synthesis in a 250 ml four-necked round-bottomedflask fitted with a KPG stirrer, internal thermometer and a refluxcooler 50.0 g of this trifluoromethanesulfonic acid-acidified,equilibrated α,ω-diacetoxypolydimethylsiloxane are mixed together with11.3 g of a molecular sieve-dried isopropanol by stirring at 22° C.Gaseous ammonia (NH₃) is then introduced to the reaction mixture untilalkaline reaction (moist universal indicator paper) and the mixture isthen stirred at this temperature for a further 45 minutes. Theprecipitated salts are separated using a pleated filter.

A colorless, clear liquid is isolated, whose accompanying ²⁹Si-NMRspectrum demonstrates the quantitative conversion of theα,ω-diacetoxypolydimethylsiloxane into anα,ω-diisopropoxypolydimethylsiloxane.

An aliquot of this α,ω-diisopropoxypolydimethylsiloxane is withdrawn andanalysed by gas chromatography. The gas chromatogram shows the followingcontents (reported in percent by mass):

Total Isopropanol D₄ D₅ D₆ (D₄-D₆) content 4.09% 2.62% 0.86% 7.57% 4.60%

Taking account of the isopropanol excess the contents of siloxane cycles(D₄, D₅ and D₆) are calculated solely based on the siloxane proportion.

Example 6 (Noninventive) Production of an Acetoxy-Terminated, LinearPolydimethylsiloxane

In a 1000 ml four-necked flask fitted with a KPG stirrer, internalthermometer and a reflux cooler 77.3 g (0.757 mol) of acetic anhydridetogether with 732.8 g (1.98 mol) of decamethylcyclopentasiloxane (D₅)are initially charged with stirring and admixed with 1.62 g (0.88 ml) oftrifluoromethanesulfonic acid (0.2 percent by mass based on the totalbatch) and swiftly heated to 150° C. The initially slightly cloudyreaction mixture is held at this temperature for 6 hours with continuedstirring.

After cooling of the batch a colorless, clear, mobile liquid isisolated, whose ²⁹Si-NMR spectrum demonstrates the presence ofSi-acetoxy groups in a yield of about 90% based on employed aceticanhydride corresponding to an α,ω-diacetoxypolydimethylsiloxane havingan average total chain length of about 14.

Conversion of the α,ω-Diacetoxypolydimethylsiloxane into theCorresponding α,ω-Diisopropoxypolydimethylsiloxane for AnalyticalCharacterization

Immediately after the synthesis in a 250 ml four-necked round-bottomedflask fitted with a KPG stirrer, internal thermometer and a refluxcooler 50 g of this trifluoromethanesulfonic acid-acidified,equilibrated α,ω-diacetoxypolydimethylsiloxane are mixed together with11.3 g of a molecular sieve-dried isopropanol by stirring at 22° C.Gaseous ammonia (NH₃) is then introduced to the reaction mixture untilalkaline reaction (moist universal indicator paper) and the mixture isthen stirred at this temperature for a further 45 minutes. Theprecipitated salts are separated using a pleated filter.

A colorless, clear liquid is isolated, whose accompanying ²⁹Si-NMRspectrum demonstrates the quantitative conversion of theα,ω-diacetoxypolydimethylsiloxane into anα,ω-diisopropoxypolydimethylsiloxane.

An aliquot of this α,ω-diisopropoxypolydimethylsiloxane is withdrawn andanalysed by gas chromatography. The gas chromatogram shows the followingcontents:

Total Isopropanol D₄ D₅ D₆ (D₄-D₆) content 1.72% 39.12% 0.88 41.72 9.50

Taking account of the isopropanol excess the contents of siloxane cycles(D₄, D₅ and D₆) are calculated solely based on the siloxane proportion.

1. A process for producing trifluoromethanesulfonic acid-acidified,end-equilibrated, acetoxy-bearing siloxanes, wherein the processcomprises reacting cyclic siloxanes, comprising D₄ and/or D₅, and/ormixtures of cyclic branched siloxanes of the D/T type with aceticanhydride using trifluoromethanesulfonic acid as catalyst and withaddition of acetic acid.
 2. The process according to claim 1, whereinthe process comprises adding acetic acid in amounts of 0.4 to 3.5percent by weight, based on the reaction matrix consisting of aceticanhydride and cyclic siloxanes comprising D₄ and/or D₅ or consisting ofacetic anhydride and mixtures of cyclic branched siloxanes of the D/Ttype or consisting of cyclic siloxanes comprising D₄ and/or D₅ andmixtures of cyclic branched siloxanes of the D/T type.
 3. The processaccording to claim 1, wherein mixtures of cyclic branched siloxanes ofthe D/T type consisting of siloxanes comprising D and T units and whose²⁹Si NMR spectroscopy-determinable cumulative proportion of D and Tunits comprising Si-alkoxy and/or SiOH groups present in the siloxanematrix is ≤2 mole percent, and contain at least 5 percent by weight ofsiloxane cycles.
 4. The process according to claim 1, wherein mixturesof cyclic branched siloxanes comprising exclusively D and T units whose²⁹Si NMR spectroscopy-determinable cumulative proportion of D and Tunits comprising Si-alkoxy and/or SiOH groups present in the siloxanematrix is greater than 2 and less than 10 mole percent are employed. 5.The process according to claim 1, wherein trifluoromethanesulfonic acidis employed in amounts of 0.1 to 1.0 percent by mass, based on thereaction matrix consisting of acetic anhydride and cyclic siloxanes, inparticular comprising D₄ and/or D₅, and/or mixtures of cyclic branchedsiloxanes of the D/T type.
 6. The process according to claim 1, whereinthe reaction is carried out in a temperature range of 140° C. to 160° C.and over a duration of 4 to 8 hours.
 7. A trifluoromethanesulfonicacid-acidified, end-equilibrated linear α,ω-acetoxy-bearing siloxaneproduced by a process according to claim 1, wherein thetrifluoromethanesulfonic acid-acidified, end-equilibrated linearα,ω-acetoxy-bearing siloxane have total cycles contents defined as thesum of the content fractions of the cyclic siloxanes comprising D₄, D₅and D₆ based on the siloxane matrix and determined by gas chromatographyafter their derivatization to afford the corresponding linearα,ω-isopropoxysiloxanes of less than 13 percent by weight.
 8. Atrifluoromethanesulfonic acid-acidified, end-equilibrated branchedacetoxy-bearing siloxane produced by a process according to claim 1,wherein the trifluoromethanesulfonic acid-acidified, end-equilibratedbranched acetoxy-bearing siloxane has total cycles contents defined asthe sum of the content fractions of the cyclic siloxanes comprising D₄,D₅ and D₆ based on the siloxane matrix and determined by gaschromatography after their derivatization to afford the correspondingbranched isopropoxysiloxanes of less than 8, percent by weight.
 9. ASiOC-bonded polyether siloxane comprising the trifluoromethanesulfonicacid-acidified acetoxy-bearing siloxane according to claim
 7. 10. Theprocess according to claim 1, wherein the process comprises addingacetic acid in amounts of 0.5 to 3 percent by weight, based on thereaction matrix consisting of acetic anhydride and cyclic siloxanescomprising D₄ and/or D₅ or consisting of acetic anhydride and mixturesof cyclic branched siloxanes of the D/T type or consisting of cyclicsiloxanes comprising D₄ and/or D₅ and mixtures of cyclic branchedsiloxanes of the D/T type.
 11. The process according to claim 1, whereinthe process comprises adding acetic acid in amounts of 0.8 to 1.8percent by weight, based on the reaction matrix consisting of aceticanhydride and cyclic siloxanes comprising D₄ and/or D₅ or consisting ofacetic anhydride and mixtures of cyclic branched siloxanes of the D/Ttype or consisting of cyclic siloxanes comprising D₄ and/or D₅ andmixtures of cyclic branched siloxanes of the D/T type.
 12. The processaccording to claim 1, wherein the process comprises adding acetic acidin amounts of 1.0 to 1.5 percent by weight, based on the reaction matrixconsisting of acetic anhydride and cyclic siloxanes comprising D₄ and/orD₅ or consisting of acetic anhydride and mixtures of cyclic branchedsiloxanes of the D/T type or consisting of cyclic siloxanes comprisingD₄ and/or D₅ and mixtures of cyclic branched siloxanes of the D/T type.13. The process according to claim 1, wherein mixtures of cyclicbranched siloxanes of the D/T type consisting of siloxanes comprising Dand T units and whose ²⁹Si NMR spectroscopy-determinable cumulativeproportion of D and T units comprising Si-alkoxy and/or SiOH groupspresent in the siloxane matrix is less than 1 mole percent, and containat least 5 percent by weight of siloxane cycles.
 14. The processaccording to claim 1, wherein mixtures of cyclic branched siloxanes ofthe D/T type consisting of siloxanes comprising D and T units and whose²⁹Si NMR spectroscopy-determinable cumulative proportion of D and Tunits comprising Si-alkoxy and/or SiOH groups present in the siloxanematrix is less than 1 mole percent, and which preferably contain atleast 5 percent by weight of octamethylcyclotetrasiloxane (D₄),decamethylcyclopentasiloxane (D₅) or mixtures thereof, are employed. 15.The process according to claim 1, wherein trifluoromethanesulfonic acidis employed in amounts of 0.1 to 0.3 percent by mass, based on thereaction matrix consisting of acetic anhydride and cyclic siloxanes, inparticular comprising D₄ and/or D₅, and/or mixtures of cyclic branchedsiloxanes of the D/T type.
 16. The process according to claim 2, whereinthe reaction is carried out in a temperature range of from 140° C. to160° C. and over a duration of from 4 to 8 hours.
 17. The processaccording to claim 3, wherein the reaction is carried out in atemperature range of 140° C. to 160° C. and over a duration of from 4 to8 hours.
 18. The trifluoromethanesulfonic acid-acidified,end-equilibrated linear α,ω-acetoxy-bearing siloxane of claim 7 whereinthe trifluoromethanesulfonic acid-acidified, end-equilibrated linearα,ω-acetoxy-bearing siloxane have total cycles contents defined as thesum of the content fractions of the cyclic siloxanes comprising D₄, D₅and D₆ based on the siloxane matrix and determined by gas chromatographyafter their derivatization to afford the corresponding linearα,ω-isopropoxysiloxanes of less than 12 percent by weight.
 19. Atrifluoromethanesulfonic acid-acidified, end-equilibrated branchedacetoxy-bearing siloxane produced by a process according to claim 8,wherein the trifluoromethanesulfonic acid-acidified, end-equilibratedbranched acetoxy-bearing siloxane has total cycles contents defined asthe sum of the content fractions of the cyclic siloxanes comprising D₄,D₅ and D₆ based on the siloxane matrix and determined by gaschromatography after their derivatization to afford the correspondingbranched isopropoxysiloxanes of less than 7 per l
 20. A SiOC-bondedpolyether siloxane comprising the trifluoromethanesulfonicacid-acidified acetoxy-bearing siloxane according to claim 8.